/**
* 【循环依赖---@Autowired】
*
* BeanPostProcessor ： org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor
*
* org.springframework.beans.factory.config.BeanPostProcessor implementation that autowires annotated fields, setter methods, and arbitrary config methods.
* BeanPostProcessor实现，用来自动织入 注解字段...;
* Such members to be injected are detected through annotations: by default, Spring's @Autowired and @Value annotations.
* 一些成员将被检测到：Spring的@Autowired、@Value；
*
* public class AutowiredAnnotationBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter implements MergedBeanDefinitionPostProcessor, PriorityOrdered, BeanFactoryAware {
*
* public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) {}
* }
*
* 1、
* DefaultSingletonBeanRegistry#getSingleton(String beanName){
* Object singletonObject = this.singletonObjects.get(beanName);
* if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
* synchronized (this.singletonObjects) {
* singletonObject = this.earlySingletonObjects.get(beanName);
* if (singletonObject == null && allowEarlyReference) {
* ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
* if (singletonFactory != null) {
* singletonObject = singletonFactory.getObject(); === 2、
* this.earlySingletonObjects.put(beanName, singletonObject);
* this.singletonFactories.remove(beanName);
* }
* }
* }
* }
* return singletonObject;
* }
*
* 2、
* AbstractAutowireCapableBeanFactory#getEarlyBeanReference{
* Object exposedObject = bean;
* if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
* for (BeanPostProcessor bp : getBeanPostProcessors()) {
* if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
* SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
* exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
* }
* }
* }
* return exposedObject;
* }
*
* 3、
* DefaultSingletonBeanRegistry#getSingleton(String, ObjectFactory){
* ...
* singletonObject = singletonFactory.getObject();
* ...
* if (newSingleton) {
* addSingleton(beanName, singletonObject); === 4、
* }
* ...
* }
*
* 4、DefaultSingletonBeanRegistry#addSingleton{
* synchronized (this.singletonObjects) {
* this.singletonObjects.put(beanName, singletonObject);
* this.singletonFactories.remove(beanName);
* this.earlySingletonObjects.remove(beanName);
* this.registeredSingletons.add(beanName);
* }
* }
*
* 5、
* DefaultSingletonBeanRegistry#addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory){
* synchronized (this.singletonObjects) {
* if (!this.singletonObjects.containsKey(beanName)) {
* this.singletonFactories.put(beanName, singletonFactory);
* this.earlySingletonObjects.remove(beanName);
* this.registeredSingletons.add(beanName);
* }
* }
* }
*
*
* 实现思路：
*
* AbstractBeanFactory#getBean
* ->
* AbstractBeanFactory#doGetBean{
* ...
* Object sharedInstance = getSingleton(beanName); === 1、
* if (sharedInstance != null && args == null) {
* ...
* }
* else{
* ...
* if (mbd.isSingleton()) {
* sharedInstance = getSingleton(beanName, () -> { === 3、
* return createBean(beanName, mbd, args);
* }
* ...
* }
* ...
* }
* ...
* }
* ->
* DefaultSingletonBeanRegistry#getSingleton(String, ObjectFactory) -> singletonFactory.getObject()
* AbstractBeanFactory#createBean <-
* ->
* AbstractAutowireCapableBeanFactory#createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args){
* ...
* Object beanInstance = doCreateBean(beanName, mbdToUse, args);
* ...
* }
* ->
* AbstractAutowireCapableBeanFactory#doCreateBean(java.lang.String, RootBeanDefinition, java.lang.Object[]){
* ...
* instanceWrapper = createBeanInstance(beanName, mbd, args);
* ...
* boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName));
* if (earlySingletonExposure) {
* addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean)); === 5、
* }
* ...
* populateBean(beanName, mbd, instanceWrapper);
* ...
* }
* ->
* AbstractAutowireCapableBeanFactory#populateBean{
* ...
* if (hasInstAwareBpps) {
* for (BeanPostProcessor bp : getBeanPostProcessors()) {
* ...
* PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
* ...
* }
* }
* ...
* }
* ->
* AutowiredAnnotationBeanPostProcessor#postProcessProperties{
* ...
* metadata.inject(bean, beanName, pvs);
* ...
* }
* ->
* InjectionMetadata#inject{
* ...
* element.inject(target, beanName, pvs);
* ...
* }
* ->
* AutowiredAnnotationBeanPostProcessor.AutowiredFieldElement#inject{
* ...
* value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
* ...
* }
* ->
* DefaultListableBeanFactory#resolveDependency{
* ...
* result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
* ...
* }
* ->
* DefaultListableBeanFactory#doResolveDependency{
* ...
* instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
* ...
* }
* DependencyDescriptor#resolveCandidate{
* return beanFactory.getBean(beanName);
* }
* ->
* 递归
*
*
*/
